This application relates to a building heating system in which a major portion of the heat may be supplied by a heat pump, so that a relatively reduced percentage of the heat load is required to be provided by a furnace which burns fossil fuel or provides heat through the direct conversion of electricity.
Heat pumps are, of course, well known in the heating and air conditioning field. Basically, in a heat pump system, a first heat exchange member is positioned within the heating system of a building, while a second heat exchange member is positioned outside of the building. Conduit and compressor means communicate with the two heat exchange members. Depending upon the specifically arranged flow pattern between the two heat exchange members, heat can be absorbed in one of them and emitted or rejected in the other of them, so that the heat pump becomes either a home heater, drawing heat from the outside, or an air conditioner, rejecting heat to the outside.
It would be desirable to place one of the heat exchangers of a heat pump system into or adjacent to the cold air plenum of a conventional forced air furnace system. With this configuration, it becomes possible to pump heat from the heat exchanger into the warm air plenum in series or parallel relation to the normal furnace air flow, with efficient heat exchange relationship, while simultaneously operating the furnace to provide necessary auxiliary heat.
However, under the circumstance when the heat pump is in the air conditioning mode, the condensation from the heat pump in the cold air plenum will send a stream of wet air onto the heat exchanger of the furnace, which, in turn, will accelerate its rusting in a most undersirable manner.
Accordingly, by way of compromise, conventional heat exchangers of heat pump systems are placed downstream from the furnace in the warm air plenum. This means that the heat pump and the furnace cannot operate simultaneously to heat the building with good efficiency, since warmed air from the furnace passes over the heat exchanger and accordingly reduces the amount of heat emitted by the heat exchanger.
It is further known that there are unexploited sources of heat in a building, particularly, the waste heat that passes up a chimney from, for example, the furnace, plus the considerable amount of heat that is generated in the attic of a building, for example, on a sunny, winter day.
While it has been previously suggested to place a heat pump evaporator in the attic of a house (Gay U.S. Pat. No. 2,780,415), and while a chimney flue and the like has been contemplated as a source of heat (Ruff U.S. Pat. No. 2,696,085), efficient systems for the exploitation of these heat sources have not been previously developed.
In accordance with this invention, a heating system is provided in which waste heat which is normally exhausted through the chimney and/or solar heat collected in an attic structure of a building, can be recovered with a relatively high level of efficiency. Furthermore, the heat pump system of this invention can operate in conjunction and simultaneously with a furnace with good efficiency, and without the disadvantage that was previously encountered in heat pump systems, so that the operation of the furnace can be minimized to save the consumption of fossil fuel or the like. Hence, the furnace can act as an auxiliary source of heat at night or at other times when the heat pump system is inadequate to provide all necessary warmth.